Laser cutting of stents and other medical devices

ABSTRACT

A desired pattern may be cut into a stent preform by impinging a laser beam onto the stent preform. The laser beam is formed using a laser system comprising a resonator cavity for resonating laser radiation, a gain medium contained in the resonator cavity, a pump for periodically pumping the gain medium and an electro-optical modulator in communication with the resonator cavity. The laser system produces a radiation pulse for each pump period. Each radiation pulse is conditioned by suppressing at least a portion of the pulse. The pulse may also be modulated with an electro-optical modulator to produce a pulse train of ordered pulses of radiation. Each pulse train is output from the optical cavity as an output laser beam which is directed at the stent preform to cut a desired pattern in the stent preform.

This application is a continuation-in-part of U.S. application Ser. No.09/681,192 filed Feb. 15, 2001 now U.S. Pat. No. 6,563,086, the contentsof which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

A stent is a radially expandable endoprosthesis which is adapted to beimplanted in a body lumen. Stents are typically used in the treatment ofatherosclerotic stenosis in blood vessels and the like to reinforce bodyvessels and to prevent restenosis following angioplasty in the vascularsystem. They have also been implanted in urinary tracts and bile ductsand other bodily lumen. They may be self-expanding or expanded by aninternal radial force, such as when mounted on a balloon.

Delivery and implantation of a stent is accomplished by disposing thestent about a distal portion of the catheter, percutaneously insertingthe distal portion of the catheter in a bodily vessel, advancing thecatheter in the bodily lumen to a desired location, expanding the stentand removing the catheter from the lumen. In the case of a balloonexpandable stent, the stent is mounted about a balloon disposed on thecatheter and expanded by inflating the balloon. The balloon may then bedeflated and the catheter withdrawn. In the case of a self-expandingstent, the stent may be held in place on the catheter via a retractablesheath. When the stent is in a desired bodily location, the sheath maybe withdrawn allowing the stent to self-expand.

In the past, stents have been generally tubular but have been composedof many configurations and have been made of many materials, includingmetals and plastic. Ordinary metals such as stainless steel have beenused as have shape memory metals such as Nitinol and the like. Stentshave also been made of biodegradable plastic materials. Stents have beenformed from wire, tube stock, etc. Stents have also been made fromsheets of material which are rolled.

A number of techniques have been suggested for the fabrication of stentsfrom sheets and tubes. One such technique involves laser cutting apattern into a sheet of material and rolling the sheet into a tube ordirectly laser cutting the desired pattern into a tube. Other techniquesinvolve cutting a desired pattern into a sheet or a tube via chemicaletching or electrical discharge machining.

Laser cutting of stents has been described in a number of publicationsincluding U.S. Pat. No. 5,780,807 to Saunders, U.S. Pat. No. 5,922,005to Richter and U.S. Pat. No. 5,906,759 to Richter.

Most solid state lasers used for cutting purposes work in a free runningregime. The typical temporal shape of a laser pulse is shown in FIG. 1.The laser pulse may be characterized as having three main parts. Themost intense part of the pulse, labeled as B in FIG. 1, causes fastheating of a metal or other material within the laser beam, melting,splashing or evaporating the material which is useful for cutting. Theinitial part of the pulse, labeled as A and the tail end of the pulse,labeled as C, produce heating and melting of materials such as metalscausing recrystallization of the metal and microcracks and is not aseffective in cutting as the more intense portion of the beam. In orderto reduce the formation of microcracks, it is desirable to condition thelaser beam to transform the less intense portions of the beam intointense spikes of laser radiation.

All US patents and applications and all other published documentsmentioned anywhere in this application are incorporated herein byreference in their entirety.

Without limiting the scope of the invention a brief summary of theclaimed embodiments of the invention is set forth below in accordancewith 37 C.F.R. 1.73. Additional details of the summarized embodiments ofthe invention and/or additional embodiments of the invention may befound in the Detailed Description of the Invention below.

A brief abstract of the technical disclosure in the specification isprovided as well only for the purposes of complying with 37 C.F.R. 1.72.The abstract is not intended to be used for interpreting the scope ofthe claims.

SUMMARY OF INVENTION

The present invention in one embodiment is directed to a method ofprocessing a stent preform comprising the steps of providing a stentpreform and a laser system which outputs a laser beam, directing thelaser beam at the stent preform and impinging the laser beam onto thestent preform to cut a desired pattern in the stent preform. The lasersystem used in accordance with the inventive method comprises aresonator cavity for resonating laser radiation, a gain medium containedin the resonator cavity and a pump for periodically pumping the gainmedium. A radiation pulse is produced for each pump period. Eachradiation pulse is conditioned to produce a pulse train of orderedpulses of radiation with each pulse train being output from theresonator cavity as an output laser beam.

In another embodiment, the invention is directed to a method ofprocessing a stent preform comprising the steps of providing a stentpreform and a laser system which outputs a laser beam, directing thelaser beam at the stent preform and impinging the laser beam onto thestent preform to cut a desired pattern in the stent preform. The lasersystem used in accordance with the inventive method comprises an opticalcavity for resonating laser radiation, a gain medium contained in theoptical cavity and a pump for periodically pumping the gain medium. Aradiation pulse is produced for each pump period. Each radiation pulseis conditioned to produce a pulse train of ordered pulses of radiationwith each pulse train being output from the optical cavity as an outputlaser beam.

In another embodiment, the invention is directed to a method ofmanufacturing a stent comprising the steps of providing a stent preformin the form of a tube or a sheet and providing a laser system comprisingan optical cavity for resonating laser radiation, an optical gain mediumcontained in the optical cavity and an optical pump for periodicallypumping the optical gain medium. The laser system produces a radiationpulse for each pump period. The method further comprises the step ofconditioning each radiation pulse to produce a pulse train of orderedpulses of radiation which are directed at the stent preform and impingedonto the stent preform to cut a desired pattern in the stent preform.Where the preform is a sheet, the sheet is then formed into a tube.

In another embodiment, the invention is directed to a method of treatinga stent comprising the steps of providing a stent, providing a lasersystem comprising an optical cavity for resonating laser radiation, anoptical gain medium contained in the optical cavity and an optical pumpfor periodically pumping the optical gain medium. The laser systemproduces a radiation pulse for each pump period. The method furthercomprises the step of conditioning each radiation pulse to produce apulse train of ordered pulses of radiation. Each of the pulse trains isdirected at desired portions of the stent and impinged onto desiredportions of the stent. The pulse trains may be characterized by anamplitude, a pulse width, an inner train separation time betweensubsequent pulses in a pulse train, and an inter train separation timebetween subsequent pulse trains. In certain embodiments, the pulses maybe conditioned using an electro-optical modulator which forms a part offeedback loop. The amplitude, pulse width, inner train separation timeand inter train separation time are selected to polish, harden orengrave those portions of the stent impinged by the pulse trains.

In another embodiment, the invention is directed to a method of treatinga workpiece comprising the steps of providing a workpiece and providinga laser system comprising an optical cavity for resonating laserradiation, an optical gain medium contained in the optical cavity and anoptical pump for periodically pumping the optical gain medium. The lasersystem produces a radiation pulse for each pump period. Each radiationpulse is conditioned to produce a pulse train of ordered pulses ofradiation, directed at desired portions of the workpiece and impingedonto desired portions of the workpiece. In certain embodiments, thepulses may be conditioned using an electro-optical modulator which formsa part of a feedback loop and the pulse trains may be characterized byan amplitude, a pulse width, an inner train separation time betweensubsequent pulses in a pulse train, and an inter train separation timebetween subsequent pulse trains. The amplitude, pulse width, inner trainseparation time and inter train separation time are selected to performa treatment selected from the group consisting of engraving, hardening,cutting and polishing.

The invention is also directed to an image processing head for use witha laser. The head comprises a housing having a first opening therein foran input laser beam and a second opening therein for an output laserbeam, a first mirror located within the housing, a second mirror locatedwithin the housing, a third mirror located within the housing and anoptical path extender located within the housing. The first mirrorredirects the input laser beam into the optical path extender. Thesecond mirror redirects the laser beam from the optical path extender tothe third mirror and the third mirror redirects the laser beam throughthe second opening in the housing.

The invention is also directed to a method of processing a stent preformcomprising the steps of providing a stent preform, providing a lasersystem which produces a radiation pulse for each pump period. The lasersystem comprises a) a resonator cavity for resonating laser radiation b)a gain medium contained in the resonator cavity and c) a pump forperiodically pumping the gain medium. The method further comprises thesteps of conditioning the radiation pulse by suppressing a portion of,but not the entirety of the radiation pulse to produce conditionedradiation, outputting the conditioned radiation in the form of a laserbeam, directing the laser beam at the stent preform and impinging thelaser beam onto the stent preform to cut a desired pattern in the stentpreform.

The invention is also directed to a method of processing a medicaldevice preform comprising the steps of providing a medical devicepreform, providing a laser system comprising a resonator cavity forresonating laser radiation, a gain medium contained in the resonatorcavity and a pump for periodically pumping the gain medium where thelaser system producing a radiation pulse for each pump period,conditioning the radiation pulse by suppressing a portion of, but notthe entirety of the radiation pulse to produce conditioned radiation,outputting the conditioned radiation in the form of a laser beam,directing the laser beam at the medical device preform, and impingingthe laser beam onto the medical device preform to modify the surface ofthe medical device preform.

Additional details and/or embodiments of the invention are discussedbelow.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 depicts free lasing radiation as a function of time.

FIG. 2 is a schematic depiction of a laser system for use in theinventive method.

FIG. 3 a depicts the output of a pump for pumping a laser.

FIG. 3 b depicts the output of a pumped free lasing laser.

FIG. 3 c depicts the output of a periodically pumped Q-switch laser.

FIG. 3 d depicts the output of a laser modulated in accordance with theinventive methods.

FIG. 3 e depicts the time varying voltage supplied to a modulator inaccordance with the invention.

FIG. 4 is a schematic depiction of another embodiment of a laser systemfor use in the inventive method.

FIG. 5 depicts an inventive image processing head.

FIG. 6 depicts free lasing radiation that has been conditioned.

FIG. 7 illustrates a series of pulse trains generated by modulating afree-lasing pulse.

FIG. 8 illustrates a series of pulse trains generated by modulating afree-lasing pulse.

DETAILED DESCRIPTION

While this invention may be embodied in many different forms, there areshown in the drawings and described in detail herein specificembodiments of the invention. The present disclosure is anexemplification of the principles of the invention and is not intendedto limit the invention to the particular embodiments illustrated.

For the purposes of this disclosure, like reference numerals in thefigures shall refer to like features unless otherwise indicated.

The present invention, in some of its embodiments, provides methods formanipulating laser beams for cutting stent preforms, stents and otherworkpieces. The invention also provides for laser systems for generatingthe laser beams used in the practice of the inventive methods.

In one embodiment, the present invention is directed to a method ofprocessing a stent preform using a laser beam. The stent preform may bein the form of a tube, a sheet or any other shape of material into whicha stent design is cut. Desirably, the stent preform will be made ofmetal. Typical metals include stainless steel and Nitinol. Othersuitable materials for the stent preform include polymeric material, asare known in the art.

The laser system used in accordance with the inventive method comprisesa resonator cavity for resonating laser radiation, a gain mediumcontained in the resonator cavity and a pump for periodically pumpingthe gain medium. The gain medium is periodically pumped and a radiationpulse is produced for each pump period. Each radiation pulse isconditioned to produce a pulse train of ordered pulses of radiation witheach pulse train being output from the resonator cavity as an outputlaser beam. The laser beam is directed towards the stent preform andimpinged onto the stent preform to cut a desired pattern into the stentpreform. The laser beam may be moved relative to the stent preform orthe stent preform may be moved relative to the laser beam.

Where the preform is in the form of a sheet, once the desired patternhas been cut into the preform, the preform may be rolled into tubularform. Desirably, the edges of the tube may be joined together viawelding, the use of adhesives or otherwise.

A number of different laser systems may be used in the practice of theinventive method. One such laser system is shown schematically at 15 inFIG. 2. Laser system 15 comprises a resonator cavity 20 which isprovided with a gain medium therein. A number of different gain mediamay be used in the laser. Desirably, the gain medium will be chosen toproduce a beam in a wavelength range of 1030 nm to 2000 nm and moredesirably, 1030 nm to 1070 nm. This may be achieved using, for example,a Yb³⁺, Er³⁺, or Ho³⁺ laser. Mirrors 25 are located at either end of theresonator. Resonator cavity 20 further comprises a modulator 30 incommunication with pulse generator 18, an aperture 32 and a polarizer35. An additional KTP crystal 40 for second harmonic generation isprovided to transform a sample of the fundamental mode energy intovisible radiation to facilitate alignment of the laser. The gain mediumis pumped with a pump 38. Desirably, the pump will be pulsed. The pumpmay also be continuous wave (cw).

A Nd-Yag (Neodymium-Yttrium Aluminum Garnet) laser may also be used inthe practice of the invention. In order to avoid losses due tobirefringence of the Nd-Yag crystal, it may prove desirable to uniformlypump the Nd-Yag laser rod via diode pumping of the Nd-Yag laser rod.Losses due to birefringence may also be mitigated by varying the shapeand/or the shape of the crystal, optionally in conjunction with the useof diode pumping of the crystal. For example, crystals of a shorterlength may result in less birefringence than crystals of a longerlength. By diode pumping, it may also be possible to achieve a smallerspot size

Samples of the output laser beam 45 are provided using mirrorarrangement 50 which splits output laser beam 45 into a main component45 a and a first sample component 45 b. Mirror arrangement 50 includesmirrors 51 and beam splitter 53 and may be made using conventionaloptical elements. Sample component 45 b is directed through apertures 57and lens with attenuator 59 to photoelement 55 for monitoring the beam.Main component 45 a is output toward the stent preform.

The operation of the laser may be further understood with reference toFIGS. 3 a-d. When operated in a free lasing regime, during any givenpump period 110, shown in FIG. 3 a, a pulse of laser radiation 120 suchas that shown in FIG. 3 b will be emitted from the laser. The pulse ischaracterized by random oscillations 124 in the intensity of the beam.

When operated with a Q-switch, as shown in FIG. 3 c, the laser willproduce a single, high intensity beam 130. A Q-switch operates bymaintaining the Q of the cavity low while a population inversion iscreated in the gain medium as a result of pumping. The low cavity Qprevents the laser from lasing. At a desired time, after a desiredamount of energy is stored, the Q of the cavity is rapidly increasedthereby facilitating stimulated emission of the gain medium. A largepulse of laser radiation is emitted. Unlike during free lasing, theQ-switched pulse decreases in intensity without random fluctuations.

In the inventive regime, as shown in FIG. 3 d, multiple pulses ofradiation 140 are produced during each pump period. Specifically, aperiodic voltage is applied to the modulator. Desirably, the modulatorwill comprise a pockels cell. Other suitable electro-optical modulatorsas known in the art may also be used. The modulator is constructed andarranged such that on the application of a negative voltage thereto, theresonator cavity is closed. When zero voltage is applied to themodulator, the cavity is open, and the optical pulse can be switched outof the cavity as shown in FIG. 3 e. By pulsing the voltage applied tothe modulator, a series of laser pulses may be generated.

Desirably, the pulses will be up to 5 microseconds long. The exact pulselength depends on the choice of metal or other material being cut. Forstainless steel, pulse lengths up to 5 microseconds in length inconjunction with an optical pump rate of 200-250 kHz are desirable. ForNitinol, pulse lengths up to 5 microseconds in length in conjunctionwith an optical pump rate of less than 200 kHz are desirable.

In applying the laser beam to the stent preform to cut a desired patterntherein, the stent preform may be moved relative to the laser beam orthe laser beam may be moved relative to the stent preform. In the formercase, the stent may be placed on a mandril and rotated and/or moved inlongitudinal direction relative to the stent preform. In the lattercase, the laser itself may be rotated about the stent preform and/ordisplaced longitudinally relative to the stent preform.

In another embodiment of the invention, a laser system such as thatdescribed above and shown in FIG. 2 may be modified to operate in anegative feedback mode. The laser system of FIG. 4 includes all of theelements of the laser system of FIG. 2 and further includes anadditional beam splitter 54 which produces another sample component 45 cof laser beam 45. Sample component 45 c is directed through attenuators58, lenses 61 and strong current photoelement 60 which is in electricalcommunication with pulse generator 18 and modulator 30. As the gainmedium begins to lase, sample component 45 c is converted via photoelement 60 into an electrical signal which causes modulator 30 toprevent substantially all of the radiation in the cavity from exitingthe cavity. In the meantime, with the absence of any radiation enteringthe photoelement and the absence of any voltage on the modulator, cavity20 opens again, and a new pulse of laser radiation is emitted therefrom.The feedback loop is allowed to continue for a desired period of timethereby producing a series of laser pulses.

The above described negative feedback loop laser system may be used totreat a stent. A stent is provided along with a negative feedback looplaser system as described above. The pulse trains output by the lasermay be characterized by an amplitude, a pulse width, an inner trainseparation time between subsequent pulses in a pulse train, and an intertrain separation time between subsequent pulse trains. The pulses may beconditioned using an electro-optical modulator which forms a part offeedback loop and the amplitude, pulse width, inner train separationtime and inter train separation time selected to polish, harden orengrave those portions of the stent impinged by the pulse trains.

As an example, a stent pattern was cut into a Nitinol tube using a pulsetrain generated as described above. Pulses of one to two nanoseconds induration with a pulse repetition rate on the order of at least 250 kHzor more were used. An assist gas such as oxygen in conjunction withcompressed nitrogen (for cooling) was used in the cutting process. Othersuitable assist gases including Ar, He or mixtures of gasses may be usedin place of or in addition to oxygen. Other inert gases may besubstituted for the nitrogen gas as a coolant. Water may also be used tocool the stent. Following cutting of the tube, the kerf had a smooth andclean appearance. The heat affected zone adjacent to the cut appearnarrower than the heat affected zone adjacent to cuts made using freelasing pulses. The dross and the slugs were of a deep black color and ofa dense powder consistency which could be removed easily from thesurface of the stent. The color and consistency differed from that whichwould result from cutting in a free lasing regime.

Without being bound by theory, it is believed that the relatively short,intense laser pulses produce an intense heating to high temperatures ofa limited volume of metal thereby causing melting, evaporation andexpulsion of metal from the surface impinged by the beam beyond thatwhich results from the spikes associated with free lasing. Relativelysmall portions of overheated metal in the oxygen flow burns andprecipitates as a powder on the metal surface resulting in a much finerstructure of striations, if any, on the surface of the kerf. This inturn results in a reduction of microcracks with the attendant increasein mechanical durability of the struts of the stent. The energy densityassociated with the free lasing regime, in comparison, results inmelting and recrystallization of metals in the melted metal bath withincreased prevalence of striations, microcracks and a reduceddurability.

Desirably, the pulses will be of no more than 2 microseconds induration. More desirably, the pulses will be of no more than 1microsecond in duration.

More generally, the invention is directed to a method of treating aworkpiece comprising the steps of providing a workpiece and providing alaser system comprising an optical cavity for resonating laserradiation, an optical gain medium contained in the optical cavity, anoptical pump for periodically pumping the optical gain medium, the lasersystem producing a radiation pulse for each pump period. Each radiationpulse is conditioned to produce a pulse train of ordered pulses ofradiation, directed at desired portions of the workpiece and impingedonto desired portions of the workpiece. In certain embodiments, thepulses may be conditioned using an electro-optical modulator which formsa part of feedback loop and the pulse trains may be characterized by anamplitude, a pulse width, an inner train separation time betweensubsequent pulses in a pulse train, and an inter train separation timebetween subsequent pulse trains and the amplitude, pulse width, innertrain separation time and inter train separation time are selected toperform a treatment selected from the group consisting of engraving,hardening, cutting and polishing.

In another embodiment, the invention is directed to a method of treatinga stent comprising the steps of providing a stent, providing a lasersystem comprising an optical cavity for resonating laser radiation, anoptical gain medium contained in the optical cavity and an optical pumpfor periodically pumping the optical gain medium. The laser systemproduces a radiation pulse for each pump period. Each radiation pulse isconditioned to produce a pulse train of ordered pulses of radiation.Each of the pulse trains is directed at desired portions of the stentand impinged onto desired portions of the stent. The pulse trains may becharacterized by an amplitude, a pulse width, an inner train separationtime between subsequent pulses in a pulse train, and an inter trainseparation time between subsequent pulse trains. In certain embodiments,the pulses may be conditioned using an electro-optical modulator whichforms a part of feedback loop and the amplitude, pulse width, innertrain separation time and inter train separation time selected topolish, harden or engrave those portions of the stent impinged by thepulse trains.

In another embodiment, the invention is directed to a method of treatinga workpiece comprising the steps of providing a workpiece and providinga laser system comprising an optical cavity for resonating laserradiation, an optical gain medium contained in the optical cavity, anoptical pump for periodically pumping the optical gain medium, the lasersystem producing a radiation pulse for each pump period. Each radiationpulse is conditioned to produce a pulse train of ordered pulses ofradiation, directed at desired portions of the workpiece and impingedonto desired portions of the workpiece. In certain embodiments, thepulses may be conditioned using an electro-optical modulator which formsa part of feedback loop and the pulse trains may be characterized by anamplitude, a pulse width, an inner train separation time betweensubsequent pulses in a pulse train, and an inter train separation timebetween subsequent pulse trains and the amplitude, pulse width, innertrain separation time and inter train separation time are selected toperform a treatment selected from the group consisting of engraving,hardening, cutting and polishing.

The invention also contemplates other embodiments in which laser pulsesare conditioned by suppressing desired portions of the pulse andsuitably conditioning the remainder of the pulse.

To that end, it is within the scope of the invention to suppress eitherthe leading edge and/or the trailing edge of a laser pulse andoptionally conditioning the remainder of the pulse and using theresulting radiation to cut a medical device such as a stent. Forexample, a laser pulse may be generated and an electrooptical modulatorused to suppress the leading edge of the pulse, denoted by A in FIG. 1as well as the trailing edge of the pulse, labeled by C in FIG. 1. FIG.6 shows a suppressing pulse (curve 100) and the resulting pulse shape(curve 200) plotted as a function of time. A plurality of such pulsesmay be generated and directed at a workpiece for manufacturing a medicaldevice. Each pulse may also be further conditioned using theabove-disclosed techniques to create a pulse train from each pulse.Using the apparatus discussed above, during free lasing, a periodicvoltage may applied to a modulator, such as, for example, a pockelscell. The modulator is constructed and arranged such that on theapplication of a negative voltage thereto, the resonator cavity isclosed. When zero voltage is applied to the modulator, the cavity isopen, and the optical pulse can be switched out of the cavity as shown.By pulsing the voltage applied to the modulator, a series of laserpulses may be generated from the free lasing pulse.

FIG. 7 illustrates a series of pulse trains generated by modulating afree-lasing pulse. As shown in FIG. 7, free lasing is suppressed via theuse of a suppressing pulse between times A and B. At time B, modulationof the laser pulse is commenced resulting in a pulse train. As shown atcurve 200 in FIG. 7, a series of pulse trains is produced. The generatorpulses are shown at curve 100. FIG. 7 shows the intensity of the pulsesas a function of time.

FIG. 8 also illustrates a series of pulse trains generated by modulatinga free-lasing pulse similar to FIG. 7. As in FIG. 8, the generatorpulses are shown in curve 100 and the series of pulse trains is shown atcurve 200. FIG. 8 differs from FIG. 7 in that a longer optical pumppulse is being used.

Without being bound by theory, it is believed to be desirable, whenlaser cutting a metal workpiece, to bring the region to be cut to itsmelting point as quickly as possible without heating adjacent regions.Where the region to be cut is heated to less than its melting point forexcessive periods of time, undesirable heat conduction into adjacentregions may result. In the case of Nitinol workpieces, this heating canresult in regions around the area to be cut having alterations in theirshape memory properties. It also may result in high stress areas andcrack initiation points. Elimination of the leading edge and trailingedges of the laser pulse, which are not believed to provide sufficientenergy to melt the metal, would reduce the extent of undesirable heatconduction and the resulting damage that it may cause.

More generally, the invention in one embodiment is directed to a methodof processing a stent preform comprising the steps of providing a stentpreform, providing a laser system which produces a radiation pulse foreach pump period. The laser system comprises a) a resonator cavity forresonating laser radiation b) a gain medium contained in the resonatorcavity and c) a pump for periodically pumping the gain medium. Themethod further comprises the steps of conditioning the radiation pulseby suppressing a portion of, but not the entirety of the radiation pulseto produce conditioned radiation, outputting the conditioned radiationin the form of a laser beam, directing the laser beam at the stentpreform and impinging the laser beam onto the stent preform to cut adesired pattern in the stent preform.

Typically, the stent preform will be a tube and desirably, a tube madeof Nitinol or stainless steel. The stent preform may also be a sheet ofmaterial, in which case the method further comprises the step of formingthe sheet into a tube subsequent to the impinging step.

Optionally, only the beginning of the pulse or a portion thereof issuppressed. It is also within the scope of the invention for only theend of the pulse or a portion thereof to be suppressed or for both thebeginning and the end of the pulse to be suppressed or portions thereof.The beginning of the pulse refers to that portion of the pulse, from thestart of the pulse, which is capable of heating the substrate to betreated (i.e. the preform) but not of melting the substrate. The end ofthe pulse refers to that portion of the pulse, which, once melting hasoccurred, is capable of heating the substrate to be treated (i.e. thepreform) but not of melting the substrate.

The conditioning step may further comprise conditioning each radiationpulse to produce a pulse train of ordered pulses of radiation for eachradiation pulse as disclosed above in this disclosure.

The invention is also directed to a method of processing a medicaldevice preform comprising the steps of providing a medical devicepreform, providing a laser system comprising a resonator cavity forresonating laser radiation, a gain medium contained in the resonatorcavity and a pump for periodically pumping the gain medium where thelaser system producing a radiation pulse for each pump period,conditioning the radiation pulse by suppressing a portion of, but notthe entirety of the radiation pulse to produce conditioned radiation,outputting the conditioned radiation in the form of a laser beam,directing the laser beam at the medical device preform, and impingingthe laser beam onto the medical device preform to modify the surface ofthe medical device preform.

Typically, the medical device preform will be a tube and desirably, atube made of Nitinol or stainless steel. The medical device preform mayalso be a sheet of material, in which case the method further comprisesthe step of forming the sheet into a tube subsequent to the impingingstep.

Optionally, only the beginning of the pulse or a portion thereof issuppressed. It is also within the scope of the invention for only theend of the pulse or a portion thereof to be suppressed or for both thebeginning and the end of the pulse to be suppressed or portions thereof.The beginning of the pulse refers to that portion of the pulse, from thestart of the pulse, which is capable of heating the substrate to betreated (i.e. the preform) but not of melting the substrate. The end ofthe pulse refers to that portion of the pulse, which, once melting hasoccurred, is capable of heating the substrate to be treated (i.e. thepreform) but not of melting the substrate. Desirably, during theimpinging step, a desired pattern is cut into the medical devicepreform.

The conditioning step may further comprise conditioning each radiationpulse to produce a pulse train of ordered pulses of radiation for eachradiation pulse as disclosed above in this disclosure.

The methods disclosed herein may be used to cut any pattern into a stentpreform or stent. Examples of stent patters are shown in WO 9626689 andU.S. Pat. No. 5,972,018.

The invention is also directed to an image processing head, showngenerally at 200 in FIG. 5. Head 200 includes a mask 202 first mirror205, an optical path expander 210, a second mirror 215 and a thirdmirror 220. Beam 45 a generated by a laser (not shown) enters head 200and is redirected by mirror 205 into optical path expander 210. Opticalpath expander consists of two mirrors 212 and 214. Beam 45 a bouncesbetween mirrors 210 and 215 until it exits optical path expander 210 andis redirected out of the head by mirrors 215 and 220. Mirrors 205, 215and 220 are desirably high reflectance mirrors. Similarly, mirrors 212and 214 are also desirably high reflectance mirrors. The configurationand number of reflecting mirrors may be changed depending on thegeometry of the housing. Beam 45 a may be focused with a variety oflenses 240 in nozzle 245 prior to exiting the head and impinging onworkpiece 247. Any suitable nozzle design may be used. The inventiveimage processing head may be used in any of the above embodiments of theinvention. It has been found that using the inventive processing head,the optimal focus position was much less sensitive to both the apertureand focusing lens position.

Any of the inventive processes disclosed above may be used as a standalone process or may be used in conjunction with other laser cuttingprocesses. For example, the inventive processes may be used inconjunction with a cooling process in which a coolant such as awater-oil mixture is pumped through the workpiece as described in U.S.Pat. No. 5,073,694. Other coolants can include gas flows.

The above disclosure is intended to be illustrative and not exhaustive.This description will suggest many variations and alternatives to one ofordinary skill in this art. All these alternatives and variations areintended to be included within the scope of the claims where the term“comprising” means “including, but not limited to”. Those familiar withthe art may recognize other equivalents to the specific embodimentsdescribed herein which equivalents are also intended to be encompassedby the claims.

Further, the particular features presented in the dependent claims canbe combined with each other in other manners within the scope of theinvention such that the invention should be recognized as alsospecifically directed to other embodiments having any other possiblecombination of the features of the dependent claims. For instance, forpurposes of claim publication, any dependent claim which follows shouldbe taken as alternatively written in a multiple dependent form from allprior claims which possess all antecedents referenced in such dependentclaim if such multiple dependent format is an accepted format within thejurisdiction (e.g. each claim depending directly from claim 1 should bealternatively taken as depending from all previous claims). Injurisdictions where multiple dependent claim formats are restricted, thefollowing dependent claims should each be also taken as alternativelywritten in each singly dependent claim format which creates a dependencyfrom a prior antecedent-possessing claim other than the specific claimlisted in such dependent claim below (e.g. claim 7 may be taken asalternatively dependent from any of claims 2-6; claim 8 may be taken asalternatively dependent on any of claims 2-7; etc.).

1. A method of processing a stent preform comprising the steps of: providing a stent preform; providing a laser system comprising: a) a resonator cavity for resonating laser radiation b) a gain medium contained in the resonator cavity c) a pump for periodically pumping the gain medium, the laser system producing a radiation pulse for each pump period; d) conditioning the radiation pulse by suppressing a portion of, but not the entirety of the radiation pulse to produce conditioned radiation; e) outputting the conditioned radiation in the form of a laser beam f) directing the laser beam at the stent preform; and g) impinging the laser beam onto the stent preform to cut a desired pattern in the stent preform.
 2. The method of claim 1 wherein the stent preform is a tube.
 3. The method of claim 2 wherein the tube is made of Nitinol.
 4. The method of claim 2 wherein the tube is made of at least one polymeric material.
 5. The method of claim 1 wherein the stent preform is a sheet of material, the method further comprising the step of forming the sheet into a tube subsequent to the impinging step.
 6. The method of claim 2 wherein the tube is made of stainless steel.
 7. The method of claim 1 wherein only the beginning of the pulse is suppressed.
 8. The method of claim 1 wherein only the beginning of the pulse and the end of the pulse are suppressed, a portion of the pulse between the beginning and the end not being suppressed.
 9. The method of claim 1 wherein only the end of the pulse is suppressed.
 10. The method of claim 9 wherein the laser beam is entrained in a column of water prior to being impinged against the stent perform.
 11. The method of claim 1 wherein the conditioning step further comprises conditioning each radiation pulse to produce a pulse train of ordered pulses of radiation for each radiation pulse.
 12. The method of claim 11 wherein the stent preform is formed of Nitinol.
 13. The method of claim 1 wherein during the impinging step the stent preform is moved relative to the laser beam.
 14. The method of claim 11 wherein during the impinging step the stent preform is moved relative to the laser beam.
 15. A method of processing a medical device preform comprising the steps of: providing a medical device preform; providing a laser system comprising: a) a resonator cavity for resonating laser radiation b) a gain medium contained in the resonator cavity c) a pump for periodically pumping the gain medium, the laser system producing a radiation pulse for each pump period; d) conditioning the radiation pulse by suppressing a portion of, but not the entirety of the radiation pulse to produce conditioned radiation; e) outputting the conditioned radiation in the form of a laser beam f) directing the laser beam at the medical device preform; and g) impinging the laser beam onto the medical device preform to modify the surface of the medical device preform.
 16. The method of claim 15 wherein the medical device preform is a stent preform.
 17. The method of claim 16 wherein the stent preform is tubular.
 18. The method of claim 17 wherein during the impinging step, a desired pattern is cut into the stent preform.
 19. The method of claim 15 wherein only the beginning of the pulse is suppressed.
 20. The method of claim 15 wherein only the beginning of the pulse and the end of the pulse are suppressed, a portion of the pulse between the beginning and the end not being suppressed.
 21. The method of claim 15 wherein only the end of the pulse is suppressed.
 22. The method of claim 15 wherein the conditioning step further comprises conditioning each radiation pulse to produce a pulse train of ordered pulses of radiation for each radiation pulse.
 23. The method of claim 18 wherein the conditioning step further comprises conditioning each radiation pulse to produce a pulse train of ordered pulses of radiation for each radiation pulse. 